Demonstrators hold signs at the state Capitol in Charleston, W.Va., Jan. 18. Local residents voiced their concerns about the quality of their tap water after a Jan. 9 chemical spill into the Elk River tainted the water supply.

A federal grand jury launched a criminal investigation Tuesday into the West Virginia chemical spill that left 300,000 residents in and around the state capital unable to use their water for eating, cooking, or washing, CNN reports.

The federal investigation comes amid ongoing concerns from Charleston, W.Va., residents and health officials that the tap water may not be fit for consumption despite assurances from the National Guard and the West Virginia American Water Co. that the concentration of the chemical known as MCHM is well below safety thresholds set by the Centers for Disease Control and Prevention.

West Virginia authorities first became aware of the incident on Jan. 9, when residents complained of a licorice-like odor coming from their taps. The odor was soon traced to a leaky storage tank at Freedom Industries, which contained a chemical foam used in the washing of coal. The chemical breached the primary tank as well as a secondary containment system and leached into the nearby Elk River.

State officials issued a “do not use” order that lasted for several days. While some communities were told that they could start flushing their pipes and resume using their taps beginning Jan. 14, many residents are still skeptical that the water is actually safe. State officials have continued to provide bottled water in light of those concerns.

The National Guard continues to test the water throughout the affected area, says Lawrence Messina, a spokesman for the West Virginia Department of Military Affairs and Public Safety. The CDC has established safety thresholds for the chemical known as Crude MCHM (4-methylcyclohexane methanol) at one part per million.

“Virtually all the samples that are coming back throughout the distribution system are nondetectable at 10 parts per billion, meaning that at a much more rigorous standard we are not finding the chemical,” Mr. Messina says.

However, in some areas, residents can still smell the telltale scent of licorice. That may be because the human nose can detect an odor with levels as low as five parts per billion, well below the CDC threshold, Messina says.

However, that threshold is not based on concrete scientific data, Rahul Gupta, director of the Kanawha-Charleston Health Department told the Los Angeles Times.

While MCHM’s use in the washing of coal is relatively recent, the chemical itself predates the Toxic Substances Control Act of 1976, which empowers the Environmental Protection agency to regulate and restrict the use of chemical substances.

Even if the chemical had hit the market after the enactment of TSCA, it is unlikely that the EPA would have been able to conduct the rigorous testing required to determine what level of concentration becomes harmful to human health, says Sheldon Krimsky, a professor of environmental policy at Tufts University in Medford, Mass.

“There are so many aspects of this chemical that there is no information about, including its general toxicity,” Professor Krimsky told the Monitor in a Jan. 10 interview. “They don’t have any information on human health effects.”

One scientist has suggested that the MCHM is breaking down into formaldehyde, a known carcinogen.

“I can guarantee you that citizens in this valley are, at least in some instances, breathing formaldehyde,” Scott Simonton, the vice-chairman of the West Virginia Environmental Quality Board and environmental scientist at Marshall University in Huntington, W.Va., told a legislative commission in Charleston. “They’re taking a hot shower, this stuff is breaking down to formaldehyde in the water system and they’re inhaling it.”

State officials, including the state’s top health officer have since called Dr. Simonton’s claims as “totally unfounded.”

Rightly or wrongly, Simonton and Gupta’s accusations have stoked public mistrust of the chemical industry and the state’s ability to keep people safe.

At a public hearing on Monday evening, residents described the harm to the local water supply as one more insult inflicted by the chemical industry. Proposed legislation before the House of Delegates' Health, Judiciary and Finance Committee would require regulation and inspection of storage facilities, such as the one at Freedom Industries.

“There is a decades old chemical industry in this valley, some people have even called it chemical valley,” says Messina, the state public safety spokesman. “Because that industry has had a home here, there have been incidents over the years and decades where you have had leaks or spills or accidents of one type or another.”

Freedom Industries handling of the incident hasn’t exactly engendered public trust, he adds. The company was apparently unaware of the leak until residents’ odor complaints prompted an investigation.

“Certainly, this company is aware of the scope of the crisis they have caused; nevertheless, they have repeatedly readjusted the estimated amount of chemical that they believe has leaked from the tank in question,” Messina says. “Then they disclosed that there was actually an additional chemical present as well. I would say that things like that have helped raise questions.”